The worst climbing accident in nearly two decades struck Nepal’s Mount Manaslu on Sunday morning. The mountain, the eighth highest in the world, experienced a pre-dawn avalanche that killed at least 11 people and left several more missing.

More than two dozen climbers were sleeping in their tents when the avalanche struck around 4 a.m. Those who survived reported sliding hundreds of feet in their tents yet not being able to survey the damage until an hour later when the sun rose.

“It was only a few seconds and we did not know what happened, but we had slid more than 200 meters,” experienced Italian Climber Silvio Mondinelli told The Associated Press. “All we wanted was for it to stop.”

When the dark subsided, the mountaineers saw mangled tents and bodies of injured or dead victims covering the snow. Those who did not survive consist of seven French climbers, two German, one Spaniard, and one guide from Nepal. Those still missing are said to be one Canadian and two French Nationals. Nepali rescue helicopters have spent much of Monday searching the slopes for the missing mountaineers, and other climbers and guides are looking on foot.

Although Mount Manaslu is traditionally considered a low-risk mountain, many veteran climbers have complained of increasingly irregular conditions in the Himalayas as there is less snow and more climbers on the mountains. Also, many prefer to climb in the spring as the fall climbing season comes after the monsoon rains, which can make the Himalayan weather even more unpredictable.

Nepal officials worry the accident will hurt the country’s vital tourist industry, which accounts for four percent of its gross domestic product.

“This is not good for mountaineering. It has made us alert about how to manage the size of expeditions and avoid casualties,” Tourism Ministry official Surendra Sapkota said.

The last major avalanche to occur on Mount Manaslu occurred in 1972 and killed six Koreans and 10 Nepalese guides.